Single site catalysts for the polymerization of alpha olefins were introduced in the mid 1980's. These catalysts are more active than the prior Ziegler Natta catalysts, which may lead to issues of polymer agglomeration. Additionally, static may contribute to the problem. As a result reactor continuity (e.g. fouling and also catalyst life time) may be a problem.
The kinetic profile of many single site catalysts starts off with a very high activity over a relatively short period of time, typically about the first five minutes of the reaction, the profile then goes through an inflection point and decreases rapidly for about the next five minutes and thereafter there is period of relative slower decline in the kinetic profile. This may be measured by the ethylene uptake, typically in standard liters of ethylene per minute in the reactor.
There is no prior art that the Applicant is aware of which expressly discloses a process to modify (improve) the kinetic profile of a supported single site catalyst. There are a number of patents which teach modified porous inorganic supports for polymerizations using single site catalysts. However, none of these patents expressly disclose that the kinetic profile of the resulting catalyst is modified.
U.S. Pat. No. 6,734,266 issued May 11, 2004 to Gao et al., assigned to NOVA Chemicals (International) S.A. teaches sulfating the surface of porous inorganic support with an acid, amide or simple salt such as an alkali or alkaline earth metal sulphate. The resulting treated support may be calcined. Aluminoxane and a single site catalyst are subsequently deposited on the support. The resulting catalyst shows improved activity. However, the patent fails to teach or suggest depositing zirconium sulphate on a silica support.
U.S. Pat. No. 7,001,962 issued Feb. 21, 2006 to Gao et al., assigned to NOVA Chemicals (International) S.A. teaches treating a porous inorganic support with a zirconium compound including zirconium sulphate and an acid such as a fluorophosphoric acid, sulphonic acid, phosphoric acid and sulphuric acid. The support is dried and may be heated under air at 200° C. and under nitrogen up to 600° C. Subsequently a trialkyl aluminum compound (e.g. triethyl aluminum) or an alkoxy aluminum alkyl compound (e.g. diethyl aluminum ethoxide) and a single site catalyst are deposited on the support. The specification teaches away from using aluminoxane compounds. The activity of these supports is typically lower than the activity of the catalyst of U.S. Pat. No. 6,734,266 (compare Table 5 of U.S. Pat. No. 7,001,962 with Table 2 of U.S. Pat. No. 6,734,266). The present invention eliminates the required acid reagent that reacts with the zirconium compound.
U.S. Pat. No. 7,273,912 issued Sep. 25, 2007 to Jacobsen et al., assigned to Innovene Europe Limited, teaches a catalyst which is supported on a porous inorganic support which has been treated with a sulphate such as ammonium sulphate or an iron, copper, zinc, nickel or cobalt sulphate. The support may be calcined in an inert atmosphere at 200 to 850° C. The support is then activated with an ionic activator and then contacted with a single site catalyst. The patent fails to teach aluminoxane compounds and zirconium sulphate.
U.S. Pat. No. 7,005,400 issued Feb. 28, 2006 to Takahashi assigned to Polychem Corporation teaches a combined activator support comprising a metal oxide support and a surface coating of a group 2, 3, 4, 13 and 14 oxide or hydroxide different from the carrier. The support is intended to activate the carrier without the conventional “activators”. However, in the examples the supported catalyst is used in combination with triethyl aluminum. The triethyl aluminum does not appear to be deposited on the support. Additionally the patent does not teach phosphinimine catalysts.
U.S. Pat. No. 7,442,750 issued Oct. 28, 2008 to Jacobsen et al., assigned to Innovene Europe Limited teaches treating an inorganic metal oxide support typically with a transition metal salt, preferably a sulphate, of iron, copper, cobalt, nickel, and zinc. Then a single site catalyst, preferably a constrained geometry single site catalyst and an activator are deposited on the support. The activator is preferably a borate but may be an aluminoxane compound. The disclosure appears to be directed at reducing static in the reactor bed and product in the absence of a conventional antistatic agent such as STADIS®.
U.S. Pat. No. 6,653,416 issued Nov. 25, 2003 to McDaniel at al., assigned to Phillips Petroleum Company, discloses a fluoride silica-zirconia or titania porous support for a metallocene catalyst activated with an aluminum compound selected from the group consisting of alkyl aluminums, alkyl aluminum halides and alkyl aluminum alkoxides. Comparative examples 10 and 11 show the penetration of zirconium into silica to form a silica-zirconia support. However, the examples (Table 1) show the resulting catalyst has a lower activity than those when the supports were treated with fluoride.
None of the above art suggests treating the support with an antistatic agent.
The use of a salt of a carboxylic acids, especially aluminum stearate, as an antifouling additive to olefin polymerization catalyst compositions is disclosed in U.S. Pat. Nos. 6,271,325 (McConville et al. to Univation) and 6,281,306 (Oskam et al. to Univation).
The preparation of supported catalysts using an amine antistatic agent, such as the fatty amine sold under the trademark KEMANINE AS-990, is disclosed in U.S. Pat. Nos. 6,140,432 (Agapiou et al.; to Exxon) and 6,117,955 (Agapiou et al.; to Exxon).
Antistatic agents are commonly added to aviation fuels to prevent the buildup of static charges when the fuels are pumped at high flow rates. The use of these antistatic agents in olefin polymerizations is also known. For example, an aviation fuel antistatic agent sold under the trademark STADIS™ composition (which contains a “polysulfone” copolymer, a polymeric polyamine and an oil soluble sulfonic acid) was originally disclosed for use as an antistatic agent in olefin polymerizations in U.S. Pat. No. 4,182,810 (Wilcox, to Phillips Petroleum). The examples of the Wilcox '810 patent illustrate the addition of the “polysulfone” antistatic agent to the isobutane diluent in a commercial slurry polymerization process. This is somewhat different from the teachings of the earlier referenced patents—in the sense that the carboxylic acid salts or amine antistatics of the other patents were added to the catalyst, instead of being added to a process stream.
The use of “polysulfone” antistatic composition in olefin polymerizations is also subsequently disclosed in:
1) chromium catalyzed gas phase olefin polymerizations, in U.S. Pat. No. 6,639,028 (Heslop et al.; assigned to BP Chemicals Ltd.);
2) Ziegler Natta catalyzed gas phase olefin polymerizations, in U.S. Pat. No. 6,646,074 (Herzog et al.; assigned to BP Chemicals Ltd.); and
3) metallocene catalyzed olefin polymerizations, in U.S. Pat. No. 6,562,924 (Benazouzz et al.; assigned to BP Chemicals Ltd.).
The Benazouzz et al. patent does teach the addition of STADIS™ antistat agent to the polymerization catalyst in small amounts (about 150 ppm by weight). However, in each of the Heslop et al. '028, Herzog et al. '074 and Benazouzz et al. '924 patents listed above, it is expressly taught that it is preferred to add the STADIS™ antistat directly to the polymerization zone (i.e. as opposed to being an admixture with the catalyst).
None of the above art discusses the kinetic profile of the catalyst system. One of the difficulties with high activity (“hot”) catalyst is that they tend to have a very high initial reactivity (ethylene consumption) that goes through an inflection point and rapidly decreases over about the first 10 minutes of reaction and then decreases at a much lower rate over the next 50 minutes together with fluctuations in reactor temperature. It is desirable to have a high activity catalyst (e.g. more than about 1500 grams of polymer per gram of supported catalyst normalized to 200 psig (1379 kPa) ethylene partial pressure and 90° C.) having a kinetic profile for a plot of ethylene consumption in standard liters of ethylene per minute against time in minutes, corrected for the volume of ethylene in the reactor prior to the commencement of the reaction, in a 2 liter reactor over a period of time from 0 to 60 minutes is such that the ratio of the maximum peak height over the first 10 minutes to the average ethylene consumption from 10 to 60 minutes taken at not less than 40, preferably greater than 60 most preferably from 120 to 300 data points, is less than 3.5, preferably less than 3, most preferably less than 2.
The present invention seeks to provide a catalyst having a kinetic profile as described above, optionally having reduced static and its use in the dispersed phase polymerization of olefins.